So, I'm searching through the www.spc.org [1] website when I come to this lovely page [2] with one of those stereograms. I have no problem in seeing the item inside the picture, but I don't think I see it “correctly” so to speak. I say that because while the object (in this case, a jack) does pop out, the parts that pop out are popped inward, not outward. For example, if the object is supposed to be a ball floating off the page, I see the object floating, but I see it as a bowl, not a ball. It's definitely a wierd experience.
I suspect that I see these objects “inside-out” (for lack of a better term) because my left eye is dominant (I'm lefthanded, by the way) wereas most people are right-eye dominant.
You can easily test this by holding your hands out in front of you, at arm's length, using your fingers to make a hole to view through. Focus on an object that's about 20 feet away (or further). Now, close one eye. If you can still see the object, that is your dominant eye (or conversely, if you can't see it, then your other eye is dominant).